february 2009 issue

Environment committee series
okotoks pushes the solar envelope

The innovative Drake Landing Solar Community stores heat underground for use in the winter. A technical showpiece, the project is highly subsidized — but its lessons could point the way to economical applications in the future

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JUST ANOTHER NEIGHBOURHOOD?
Liz Reese lives in what, from the street, looks like a normal suburban community. But the Drake Landing Solar Community in Okotoks is anything but normal, with a new level of technical innovation heating the space behind all those doors.

BY BILL CORBETT
Freelance Writer

Boasting the most hours of sunshine in Canada, Alberta seems the ideal candidate for a visionary solar heating project. Perhaps it’s no surprise, then, that sunny Okotoks — arguably Canada’s greenest municipality — was chosen as the site of North America’s first solar neighbourhood.

But even with all that sunshine, the 52-home pilot project known as the Drake Landing Solar Community still has to deal with Alberta winters. Like all solar space heating projects in Canada, its biggest challenge is to make sure there’s enough energy when it’s needed most, in winter.

The solar radiation available in winter simply can’t meet the demands of home heating. Drake Landing’s response is to collect solar heat during the intense sunshine months of summer, then store it in an underground reservoir. In the winter, heated water circulates to the homes.

As the project moves through its second winter of heating all those houses, the solar storage system continues to pass all technical challenges with flying colours.

Although economics are another matter for now, “we’ve shown that it’s quite possible to do this and to do it well,” says John Kokko, P.Eng., vice-president of Enermodal Engineering.

Mr. Kokko has a long history with the project. As well as being its lead engineer, he provided feasibility studies, construction review and commissioning.

Where it Began
The seeds for Drake Landing were, in fact, sown back in 2003. Natural Resources Canada was at that time searching for a community to test a seasonal underground solar storage system.

The Town of Okotoks was already a green leader, having implemented energy-efficiency initiatives, community recycling and composting, and even solar hot water systems for town buildings. Keen to add another project to its resumé, Okotoks answered the call.

Once Sterling Homes, ATCO Gas and other partners had signed on, the project was launched. The Drake Landing Solar Community’s first homeowners took possession in 2006.

Their neighbourhood appears normal — almost. The most visible part of the Drake Landing system is its 800 solar collectors. Covering more than 2,300 square metres, they’re mounted on the rear garages and breezeways of the two-storey homes.

The peak summer heating capacity of 1.6 MW produced by the collector array is transferred using a glycol solution through insulated piping to short-term heat storage. This storage occurs in a pair of huge tanks in an above-ground energy centre.

The heated water then goes subterranean. Hot water is piped into a field of 144 shallow wells in what is called a borehole thermal energy storage system, or BTES, for long-term storage. The field of wells extends 33 metres below ground and covers an area 35 metres in diameter.

The heat delivered by the piping in the wells transfers to the surrounding cooler earth. The field is covered on the top by layers of sand, R-40 insulation, a waterproof membrane, clay and landscaping.

In winter, when heat is needed, it is recovered from the BTES system and sent to the short-term storage tanks. From there, hot water is circulated through a pair of underground pipes to the houses. Within each house, a fan coil transfers heat from the hot water to the forced-air circulation system. This heat is then blown through the ductwork, just like it would be in a normal forced-air system.

European Forebears
It’s a cutting edge system, to be sure, even though seasonal solar storage is more established in Europe. No systems there, however, provide more than 70 per cent of communal space heating needs.

By contrast, Drake Landing designers wanted to expand this solar slice to an unprecedented 90 per cent — in part to help meet a target of reducing each house’s greenhouse gas emissions by five tonnes per year, when compared to conventional new homes.

Although it was expected to take five years for the BTES system to be fully charged, it has already hit 55 per cent and should reach 90 per cent within three years, says project manager Bill Wong, P.Eng., of SAIC Canada.

“The Drake Landing solar project is the first one of its kind in North America and the first in the world designed for such a high solar fraction,” says Mr. Wong. “The task was made possible by the combined efforts from a great team, with highly committed members working together, focused on achieving a common goal. It was very difficult to find anyone in North America who has worked on this type of project before.”

He continues: “The team really pulled together and learned from each other, and also learned from our European colleagues who openly shared with us their experiences and the dos and the don’ts. It has been a very rewarding experience for the entire team. I would say the learning process was one of the highlights of the project execution.”

One of the first steps to meeting the 90 per cent target was to lower the overall heat load as much as possible. Thus, the Drake Landing Solar Community is the largest subdivision of single-family houses in Canada built to R-2000 standards, making them some 30 per cent more energy efficient than conventional new houses. Each house also has its own solar hot water system, meeting about 60 per cent of its annual domestic hot water needs.

Combined with the solar storage system, these steps are expected to reduce each house’s annual grid use by 110.8 gigajoules — 93.9 from space heating and 16.9 from water heating. Space and water heating typically account for more than 80 per cent of Canadian home energy use.

“Reducing the heating load on the houses was a major thing,” says Enermodal’s Mr. Kokko. Because the efficiency of the solar heating system is about 16 per cent, “every gigajoule you can take out of the heating demand is six gigajoules of solar energy you don’t have to collect, store and distribute.”

Mr. Kokko continues: “As well, it struck us one day that the best thing we could do to get the efficiencies and heat allocation levels we wanted was to use the borehole system only for space heating and have a separate dedicated solar system for water heating on each house. This allowed the water in the underground storage system to be used at much lower temperatures than the 60 degrees Celsius required for domestic hot water.”

Making it Work
With good ideas in hand, the hard work began for a team that included a BTES designer from the Netherlands.

“One of the biggest challenges the team had was designing the borehole storage field,” says Mr. Kokko. “We had to do a lot of computer simulation to get the right number of boreholes and the right spacing and configuration of the boreholes.

“There was a lot of discussion about whether we should use single or twin tubes in the boreholes — we eventually went with single tubes. Even the grout we needed for cementing the tubes into the boreholes was not one we were familiar with.”

Other challenges included correctly sizing everything — from solar collectors to short-term storage tanks — and installing digital controls capable of continually adjusting settings on all pumps, valves and other equipment in the energy centre. These adjustments are necessary to optimize performance based on current conditions, including weather, load and energy availability.

“There were some design issues with the new type of solar collectors we were using and trying to connect 800 of them with piping,” says Mr. Wong of SAIC. “There were just a lot of little things that hadn’t been done before, and we had to work through them.”

What project proponents still grapple with are the economics of seasonal storage systems for solar space heating. Some $7 million in funding, most of it federal, went into the Drake Landing community, resulting in a subsidy of about $134,000 per house that purchasers didn’t have to bear.

“It’s very important that people approach Drake Landing as a technical project,” says Gordon Howell, P.Eng., of Edmonton-based Howell-Mayhew Engineering. Well known for his involvement in Edmonton’s Riverdale NetZero energy house, Mr. Howell was involved in early monitoring at Drake Landing.

“The costs were really high, and the project needed lots of public funding to get built,” said Mr. Howell. “But it’s like any new technology. Radio, TV, cars, airplanes, computers — they were all very expensive to begin with.”

Still, it may be a long time before systems using solar space-heating storage are economical without subsidies. While the lessons learned from Drake Landing might cut the cost of a similar project in half, it would still be far from competitive with one using natural gas today — largely because the price of natural gas is itself highly subsidized.

That isn’t stopping both SAIC Canada and Enermodal from looking at other possible Canadian projects with potential municipal and development partners. Larger subdivisions and higher-density developments, along with the great experience with the technology the companies have gathered, could bring per-unit costs down.

So, too, could hybrid systems that combine solar storage with conven-tional fuels or with other technologies such as ground-source heat pumps. Where feasible, aquifers could even be used as an underground storage medium for both heating and cooling.

But none of these alternatives promise the same greenhouse gas reductions as Drake Landing.
“This project was to see how far you could push the envelope,” says Mr. Kokko. “The next projects will probably look at the cost of energy and try to figure out what portion of solar is economically feasible.”

Adds Mr. Wong: “Now with this first project completed, we are ready to work with other energy professionals across Canada to share the learning points and try to replicate the concept where there might be a fit.”